Greater energy efficiency equals less emissions

Jun 30 2013

Today’s marine industry is placing greater emphasis on energy than ever before. This
comes as no surprise, since virtually all energy at sea comes from the burning of fuel.

Given that fuel at current prices can be up to 70% of a vessel’s operating expenses, it makes economic sense to burn less – and to get more from whatever is burned. This is putting fuel efficiency, fuel flexibility and energy recovery in the spotlight. Moreover, the fact that every penny counts is calling attention to cost of ownership and the minimisation of lifecycle costs.

In a recent paper, Alfa Laval outlined its work to merge these aspects into complete solutions for energy efficiency.

Achieving energy efficiency and thereby a reduction in fuel-related operating costs, is a key to profitability in today’s marine business. But the problem of rising fuel prices is just one incentive to burn less fuel. The other is emissions legislation, which targets HFO in particular.

Burning less HFO immediately reduces the production of CO2, SOx, NOx and other harmful emissions. But with current fuel alternatives either expensive or impractical, HFO will be the continued choice for most vessels. Scrubbers will have to do the bulk of curbing emissions, with additional fuels and fuel blending to lend a hand.

The trick, then, is to find fuel-saving solutions within the framework that already exists on board. In this respect, slow steaming is the prime example, since it allows extreme savings without changing equipment at all.

For equipment suppliers, this means new complexities. “Today we have an increasing mix of parameters to take into account,” said Alfa Laval’s Niclas Dahl, market unit manager marine energy. “Varying engine loads, multiple fuels and other factors are all interrelated in their effect on energy efficiency. So looking at individual equipment is no longer the whole answer.”

The answer, as Alfa Laval sees it, is to view energy savings in a wider perspective. “In addition optimising products and features for energy efficiency, we’re taking a step back and looking at entire process lines, both before and after the engine,” said Dahl. “By optimising the design and operation of the fuel line and the steam line, for example, we’re opening up possibilities for a new level of savings.”

The fuel line, Dahl explains, encompasses the separators, boosters and related equipment prior to the engine, including equipment for handling waste. The steam line includes the boilers, freshwater generators and heat exchangers, but also the recovery systems that reclaim energy from the engine exhaust.

The obvious part of working with the fuel line and steam line, said Dahl, is re-evaluating certain aspects based on today’s new situation. “Waste fuel oil is a good example,” Dahl said. “In the past, this was waste and nothing more. But thanks to MARPOL rule MEPC.1/Circ.642, we can now work with integrated oily waste cleaning. Using PureDry, we can recover up to 2% of the original fuel volume, leaving just a tiny amount of superdry solids and a lot of water that feeds directly into the bilge water treatment system.”

In the steam line, new solutions are becoming attractive without any new legislation. “Fuel prices are changing the way people look at waste heat recovery,” said Alfa Laval’s Dennis Verkaart, market unit manager marine boilers & heaters. “In the past, recovering waste heat from the auxiliary engines didn’t seem worth the effort. But at today’s fuel prices, Alfa Laval’s auxiliary solutions now have a payback time of less than two years.”

For vessels with the newer long stroke main engines, Verkaart pointed out, waste heat recovery from the auxiliary engines is even becoming a necessity. “More and more, we’re seeing designs where the cooler exhaust of long stroke main engines won’t meet the steam needs en route,” he said. “By integrating the auxiliary engines into the steam line, vessels can still avoid the use of the oil-fired boiler at most engine loads.”

Adaptive solutions

The more challenging aspect of working with process lines, said Dahl and Verkaart, has less to do with new applications. Instead, it has to do with the interactions between existing equipment. When the parts of a line can respond to each other, it creates an adaptive solution whose total energy consumption is lower.

“In some ways, Alfa Laval has been pioneering adaptation for years,” said Verkaart. “Our Aalborg boiler systems, for example, are individually designed to match the steam consumers they serve. By adapting the boiler’s design and performance to a specific use downstream, we can ensure the highest energy efficiency in the steam line as a whole.

“In thermal fluid installations, we’ve taken it a step further by adapting in real time. With the heat consumers connected to an Aalborg Energy Management System, the available heat can be compared with actual consumer requirements. So by prioritising the consumers and directing the heat accordingly, peak loads and use of the oil-fired boiler can be minimised,” he claimed.

In the fuel line, real-time adaptation has been an Alfa Laval focus since the introduction of Alcap. “With Alcap, we began adjusting to the nature of the oil,” said Dahl. “Today we’re doing that in an increasingly sophisticated manner, with fuel conditioning that efficiently manages the transition between fuels. Advanced cooling has been added to our high-level automation and in the near future we’ll offer solutions for fuel blending and upto- the-minute consumption monitoring.”

Alfa Laval has unveiled a new heat exchanger.

Safeguarding engine efficiency

One of today’s great paradoxes is the link between better emissions and lower fuel quality. Low-sulphur HFO, while better from an emissions perspective, is commonly produced using slurry oil from the fluidised catalytic cracker (FCC) as cutter stock. Since aluminium-silicon oxides are catalysts in the cracking process, this has led to a greatly increased content of catalytic, or cat fines.

If not removed, these fines threaten catastrophic engine failure, as they can destroy cylinder linings, piston rings and more. But cat fines are also an energy issue. Even if the engine remains operational, the wear they produce will reduce its combustion efficiency.

Today, the separators that remove cat fines operate continuously at maximum flow rate. But in the era of slow steaming, this makes little sense. Reducing separator throughput would not only lower pump-related energy consumption, but also increase separation efficiency and the margin of engine protection.

Adaptive fuel cleaning

Lowering the separator’s maximum flow rate is impossible, of course. Slow steaming vessels may increase speed for any number of reasons, which means full separator capacity must always be available. However, Alfa Laval is working on a truly adaptive system, in which the separator feed is adjusted to the engine load.

“The idea is to provide our S separator with a flexible feed of 25-100%,” said Dahl. “Based on sensor feedback from the engine, the flow from VFD-driven separator feed pumps is steplessly adjusted to match the engine load. This directly reduces the separator-related energy consumption, but it has the added benefit of enhancing the S separator’s already leading cat fine removal.”

For even greater protection, additional sensors are placed at key locations throughout the fuel line. By measuring iron and aluminium levels, these provide a realtime assessment of fuel quality and the wear due to cat fines. “Most importantly, these sensors are a tool for detecting peaks, for example when rough seas stir up cat fine sediment in the day tank,” said Dahl. “With the warning they provide, action can be taken well before large amounts of cat fines are able to enter the engine.”

This adaptive system has already been installed and is operating at sea. And according to Dahl, Alfa Laval is seeing breakthrough results: “We’ve got flexibility for slow steaming, improved engine protection and further reductions in oil losses – all while consuming less power.”

Alfa Laval’s efforts extend well beyond the design and delivery of its products, the company said. Even within the Alfa Laval Parts & Service organisation, there is a growing range of offerings focused on energy needs.

“Alfa Laval is committed to energy efficiency at all levels and all times, from the design of components, equipment and process lines to the ongoing optimisation of equipment at sea. No other marine supplier can match our breadth – either when it comes to equipment or the knowledge we have in applying it,” Verkaart claimed.

New heat exchanger

Alfa Laval has also unveiled a new heat exchanger. The new T35 gasketed plate heat exchanger is claimed to have patented performance-enhancing features.

“Shipowners consider performance, reliability and lifecycle costs as critical factors when selecting new heat exchangers for their vessels. However, the single most important factor for decision-makers is the investment cost,” said Adrian Hogan, Alfa Laval business manager, marine plate heat exchangers. “The T35 is engineered for cost-effectiveness and provides higher heat transfer efficiency, more uptime and reduced installation, operation and maintenance costs.”

Alfa Laval engineers conceived T35 to replace the company’s workhorse, the Alfa Laval M30 heat exchanger, which was introduced in 1989 and is oldest of its size on the market. In addition to central cooling, the Alfa Laval T35 may also be used for lube oil cooling and for cooling in scrubber gas applications.

Cost, efficiency and serviceability are behind the three major innovations, which make the new Alfa Laval T35 gasketed plate heat exchanger noteworthy, the company said:

Patented Alfa Laval ClipGrip gasket system optimised for high and low pressures and for quick mounting and secure positioning. The new design extends gasket lifetime and significantly lowers maintenance and replacement costs compared to gasketed plate heat exchangers that require glued gaskets.

Enhanced lightweight frame design with optimised frame thickness, two frame heights, updated marine class approval and new roller assembly and special foot attachment to make opening and closing easier. These enhancements contribute to ease of maintenance.

The CurveFlow plate pattern provides superior flow distribution with uniform flow velocities across the complete plate surface. By maintaining a low pressure drop in the plate distribution area, a greater portion of the available pressure drop is available for heat transfer.

Compared to a typical marine central cooling system with conventional plates, the upfront investment costs, as well as the operating costs, are considerably lower with the T35 and its CurveFlow plate pattern. According to estimates, the T35 can reduce pump electricity costs by up to 20% and, as a result, also lower carbon emissions.

Moreover, the new plate design also means the T35 requires less frequent maintenance and cleaning than comparable heat exchangers. This saves on spare parts, cleaning chemicals and labour-related costs. Maintenance, when required, is claimed to be quick and easy, thanks to new T35 features, including the Alfa Laval ClipGrip, five-point alignment system and swing foot.